The invention relates to an optical disc player comprising a rotatable disc-spindle and a read objective which is arranged on a movable carriage for radial translational displacement of the objective relative to an optically readable disc, which is disposed on the disc spindle, between a minimum and a maximum radial distance between which the information to be read is contained on a disc. The invention comprises a drive unit for driving the carriage by cooperation of a drive pinion and a gear rack, which drive unit comprises: a frame; connected to the frame, an electric motor with a motor spindle which is rotatable about an axis of rotation; said drive pinion, which is rotatably journalled on the frame; a gear wheel which is coaxially connected to the drive pinion; and a primary pinion for driving the gear wheel.
The applicant's copending U.S. patent application Ser. No. 713,511 refers to a disc player of the type described above, the drive unit being mounted on a carriage which also accommodates a helium/neon laser, its high-voltage ignition unit, as well as a number of optical and electronic components, including the read objective. The rotatable disc spindle is constituted by the spindle of a main motor, which is mounted on a mounting plate manufactured from sheet steel. On said sheet-steel mounting plate two guide ways are mounted relative to which the carriage can move with the aid of roller bearings provided for this purpose. A gear rack for cooperation with the drive pinion is mounted on the mounting plate (see drawing).
Said drive unit should be of an inexpensive yet reliable construction, stringent requirements being imposed on the quality of the carriage drive. For a correct operation of an optical disc player of this type, it is essential that a light beam produced by the laser is continuously focussed with great accuracy on the very small information structure on the optically readable disc by the objective. For further information relating to an optically readable video disc and the equipment to be used for reading the information contained on said disc, reference is made to a number of articles in "Philips Technical Review" volume 33, 1973, no. 7, pp. 178-193, which relate to the Philips VLP system. In particular, it is of importance that there is no play between the various gear wheels of the drive unit or between the drive pinion and the gear rack. Play between these components could give rise to problems with the automatic correction of the position of the objective and thus of the carriage relative to the information track to be read on the video disc by means of an electronic control circuit provided for this purpose. Another requirement to be imposed on the drive unit is that it should not excessively hamper the to and fro movement of the carriage during work on the disc player, for example during manufacture or in the case of maintenance activities.